The present invention relates to a drum for assembling tire components such as a breaker with a tread (in this use the drum is generally called a belt drum).
In general, a belt drum is a means used for building a belt and tread assembly as a sub-assembled tire component. The assembly is then removed from the belt drum held by a transfer ring, transferred to a shaping drum or the like, and assembled onto a toroidally shaped carcass to build a complete green tire for subsequent vulcanisation.
In order to facilitate the building on the belt drum and the removal from the belt drum of the assembly, the belt drum must be capable of increasing and reducing its outer diameter. An example of a conventional mechanism for this increase and decrease of the belt drum diameter is the air bag type mechanism shown in FIG. 6. In this case, compressed air is supplied to an expandable air bag to inflate it to displace movable drum segments bb in the radially outward direction. Reference element cc represents a rubber band for reducing the expanded outer diameter of the drum. The conventional air bag type mechanism has drawbacks in that the expandable stroke of the drum is short and the drum is insufficiently resistant to an external pressure.
Another example of a conventional mechanism for increasing and decreasing the drum diameter is a tube type mechanism (not represented in the drawings). However, this tube type mechanism has the same drawbacks as the air bag type mechanism.
Yet another known and conventional drum employs a link mechanism to provide the expanding and reducing mechanism. However, this drum has a drawback in that the resistive strength to external pressure is insufficient when the link is inclined relative to the direction of the external pressure though the strength is sufficient when the link is later positioned parallel to the direction of the external pressure.
In view of the foregoing, it is an object of the present invention to provide a drum for assembling tire components such as a breaker with a tread, which has a simple construction capable of providing a reliable expansion and shrinkage, has a sufficient structural stability to minimise any undesired movements of respective drum segments and has a much increased expandable stroke in the radial direction.